This paper describes the development of a comprehensive mathematical and numerical model for simulating the performance of automotive three-way catalytic converters, which are employed to reduce engine exhaust emissions. The model simulates the emission system behavior by using an exhaust system heat conservation and catalyst chemical kinetic submodel. The resulting governing equations are solved numerically. Good agreements were found between the numerical predictions and experimental measurements under both steady-state and transient conditions. The developed model will be used to facilitate the converter design improvement efforts, which are necessary in order to meet the increasingly stricter emission requirements.